Transcript Milky Way Center

Milky Way (-like) Galaxy
Milky Way Galaxy
Eye
1.
2.
3.
4.
Sun + Moon … EARTH AS A SPINNING PLANET
planets … SOLAR SYSTEM
nearby stars … SOLAR NEIGHBORHOOD
white haze of sky … MILKY WAY GALAXY
Greek “galactos” = milk
thickest in Sagittarius, through Cygnus, Orion
dark bands
obscuration
star clusters
nurseries
Galileo first resolved into stars
WE ARE INSIDE IT
Milky Way from Inside
Milky Way Galaxy
Members
stars
1011 to 1012
entire HR Diagram
not stars
white dwarfs, neutron stars, black holes
brown dwarfs
rocks
solar systems, planets, asteroids, KBOs, comets
gas/dust
nebulae, ISM, GMCs
life
Herschel’s Milky Way
History
pre-20th century … no idea there were “galaxies”
Herschel star count model … pre-parallaxes, HR
assumptions:
(a) Sun at center
(b) all stars identical
(c) no obscuration
result: much too small
Galactic Scales
Spiral Nebulae like Andromeda
individual baby stars
but, no parallax measured
Clues to the MW Mystery
Variable Stars
small fraction of all stars
eclipsing … two stars
novae/supernovae … sporadic
pulsating … intrinsic, regular
HR “Instability Strip”
Distance Ladder Rung #4
Shapley Solves MW Mystery
Globular
Clusters
RR Lyrae variables
found: GCs at great distances
spherically symmetric
EUREKA! … center of GCs = center of MW
Milky Way Map
Milky Way Territories
DISK
BULGE
HALO
30000 x 300 pc
100:1
4000 x 6000 pc
football
50000+ pc
spherical
details
arms
bar
edge?
origin
last
mixed
first
young Pop I
blue/white
2% metals
mixed Pops
yellow
old Pop II
red
0.02% metals
open clusters
gas/dust/* formation
massive BH
gas/dust ring
globular clusters
no gas/dust/planets
merry-go round
random spiral
electron-like
disordered
size
stars
contents
motion
Milky Way Formation
Four Phases
1. early star formation in ENORMOUS contracting cloud
GCs as substantial blobs
halo stars old
halo stars have random motion
size of halo
slight halo rotation
2. collapse of gas to disk … no gas/young stars
3. star formation in disk … young stars now
4. cannibalization of other galaxies/GCs … star streams
HALO FIRST … DISK LAST
Formation
Star Motions
Andromeda Galaxy
Spiral Arms
Tracers
21 cm emission of H atom
CO in GMCs
Scale
Sun is 8 kpc from center of MW
stars, GCs, arms, observed to radius of 15 kpc
gas observed to radius of 25 kpc
Formation?
cohesive arms would wind up and disappear …
Spiral Arms
Formation?
cohesive arms would wind up and disappear …
Density Waves gas moves into ripple
compresses
stars form
Causes
galaxy collisions?
companion galaxy tides?
bar-like asymmetry of rotating bulge?
gas instability near the bulge?
Observe
patterns not mass movement!
Spiral Traffic
Milky Way Rotation
Missing Mass
Rotation Curve orbital velocity vs. distance
curve RISES even beyond where we see stars
more mass than seen
out to 40 kpc (at least)
Missing Mass
Conclude
> twice as much mass as can be seen
dark matter dark at all wavelengths
Candidates
black holes
white dwarfs
red/brown dwarfs
subatomics
mixture?
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need lots of big stars
burned out regular stars
need lots
hard to test
Milky Way Center
center of GC distribution
center of gas distribution
8 kpc away
Milky Way Center
Contents
50000 stars/cubic parsec …
million X local!
stellar encounters and crashes
molecular gas ring, diameter 400 parsecs
Ground Zero
bright radio source
X-rays, gamma rays
hot gas at 10000 K
extended filaments
flickering
fast moving gas+stars
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Sgr A*
energetic
heating
magnetic fields
small
MASSIVE
Milky Way Center
see the movie!
Answer?
1 million Msun
0.02 AU = 4 Rsun
SUPERMASSIVE BLACK HOLE
Milky Way Today
.
THIS
IS
AN
ARTIST’S
CONCEPTION!
Milky Way Today
THIS
IS
REAL!
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